Polycarbonates have been used as materials in various fields, and as their application fields have become wider, there has arisen a demand for the development of polycarbonates having improved properties.
The electrophotographic photoreceptors that have recently been proposed and used include (1) layered-type organic electrophotographic photoreceptors, the photosensitive layers of which contain at least two layers, namely a charge generation layer for generating charge by exposure and a charge transport layer for transporting the charge, and (2) single-layer-type electrophotographic photoreceptors, the photosensitive layers of which are single layers where charge generating materials and charge transporting materials are dispersed in resins. As the resins contained in the charge transport layer of the layered-type electrophotographic photoreceptors and in the photosensitive layer of the single-layer-type electrophotographic photoreceptors, polycarbonate resins prepared from bisphenol-A have been widely used.
Since polycarbonate resins prepared from bisphenol-A have good compatibility with charge transporting materials, photoreceptors whose photosensitive layer contains such polycarbonate resins are characterized by their good electrical properties and their relatively high mechanical strength.
However, the photoreceptors produced by using the polycarbonate resins prepared from bisphenol-A have been found to involve some problems, including the following problems (1) and (2).
(1) In the production of such photoreceptors, their photosensitive layers are formed by applying a coating liquid dissolved in a solvent, and some solvents make the coating liquid get cloudy (to gel) or make the photosensitive layer crystallize easily. This causes quality defects of developed images since photo-induced discharge hardly occurs on the crystallized regions, leaving residual charges which cause an undesirable electric potential on the regions.
(2) In the case of general negatively-charged-type electrophotographic photoreceptors, their photosensitive layer formed by using the polycarbonate resins derived from bisphenol-A tends to be peeled off from their base layer due to poor adhesion to the base layer, or is worn or scored for lack of surface hardness, thereby shortening plate wear life. Herein, the base layer generally indicates the charge generation layer of layered-type photoreceptors, or the electroconductive substrate of single-layer-type photoreceptors.